It is known that various alloys having specific magnetic properties can be used for the manufacture of articles which, thanks to their magnetic properties, can be used in the electrotechnical or electronics industry, for example for the manufacture of relays, meters, transducers, etc.
In particular, alloys currently used include quaternary alloys based on iron, aluminum, nickel and cobalt which have valuable magnetic properties but which are advantageously replaced in certain cases by ternary alloys based on iron, cobalt, and chromium. Such alloys in fact have the advantage of the capability of being shaped by cutting or punching out the alloy, said alloys being in the form of elongated products such as continuous strips or wires, sheets or bars.
The magnetic properties of the alloys can be adjusted as a function of the requirements by altering, on the one hand, the composition of the alloy and, on the other hand, the heat treatments to which it is subjected. In particular, the Fe-Co-Cr alloys comprising 26 to 32% chromium and 9 to 25% cobalt have the advantage of developing magnetic properties close to those of the quaternary Fe-Al-Ni-Co alloys, and are moreover adapted to be cut and shaped, for example by punching out or forging. For this reason they are called shapeable magnets.
The heat treatments which are capable of developing the desired properties are fairly complicated and comprise different operations for heating, maintaining temperature or cooling at predetermined rates of temperature variation. However, for some time it has been observed that it is valuable to subject the magnetic alloy to an annealing operation carried out, for example, at about 650.degree. C. in the presence of a strong magnetic field greater than 160,000 A/m (2,000 Oe).
This annealing operation in the presence of a magnetic field gives very valuable results but has the disadvantage of requiring the use of an electromagnet or similar device for the production of such an intense magnetic field. For this reason, the apparatus is fairly costly and difficult to use.